A conventional front jaw is already described in AT-PS 321 170 (which corresponds to U.S. Pat. No. 3,902,730). Each toggle lever in this front jaw grips only the lateral edge of the sole of the boot. To hold the sole of the boot from above, an additional sole down-holding means is provided which must be adjusted manually in its elevational position for soles of boots having differing thicknesses. Consequently, such a handling of the front jaw is time consuming.
In the front jaw according to DE-OS 24 48 769, the housing receiving the release spring has a backside on which, in the skiing position, is supported a sole holder which is approximately circular in the top view and provides a three-point contact. The sole holder is thereby urged against the backside of the housing by a pull rod loaded by the release spring. The front jaw can be released both during a pure twisting fall and also during a backward fall and also during a backward twisting fall of the skier. The necessary release force can be changed by adjusting the initial tension of the release spring and by shifting the upper support point of the sole holder on the backside of the housing.
The aforesaid front jaw has the disadvantage that it can only be used for soles of boots having exact dimensions, since its sole holder cannot be adjusted to deviating dimensions in the thickness and in the peripheral surface of the sole of the boot.
The front jaw according to the first embodiment of DE-OS 30 20 346 (which corresponds to U.S. Pat. No. 4,345,776) (compare FIGS. 1-7) has a ski-fixed housing in which a release spring with an adjustable initial tension is housed. A pull rod extends through the spring, which pull rod terminates in a bearing eye at its end facing the ski boot. A connecting piece is stored in the bearing eye. An adjusting screw extends through the connecting piece. The two ends of the adjusting screw are supported in a sole down-holding means which, when viewed in the top view, consists of a center part extending in transverse direction with respect to the front jaw and of two legs connected to the part each at an angle. The center part is pulled toward the projecting edge of the housing by the release spring such that a three-point contact exists.
In another embodiment (compare FIGS. 8-13 of DE-OS 30 20 346), a peg is vertically fastened on the ski, on which peg is supported a housing for a release spring, which housing carries a sole down-holding means. A three-point contact exists also in this case, namely, of the housing on the peg.
The sole down-holding means can in both embodiments not only pivot in a plane parallel with respect to the upper side of the ski, but a lifting of the sole down-holding means is also possible during a backward fall of the skier. Of course, the sole down-holding means is designed as a rigid member which cannot adjust to the shape of any kind of a sole of a boot.
The front jaw according to AT-PS 315 698 (which corresponds to U.S. Pat. No. 3,950,002) does not have this disadvantage. A pull rod loaded by a pressure spring is housed in a ski-fixed housing in a first embodiment (see FIGS. 1-3). A piston equipped with an annular groove is fastened to the pull rod. The base of the housing is extended toward the ski boot and carries two vertical swivel axes on which rocking levers are supported, the longer lever arms of which rest on the sole of the boot. The shorter lever arms of the two swivel levers engage the annular groove of the piston.
A type of pivot pin engaging bore is provided in the shorter lever arm of each of the two rocking, which shorter lever arm rests in a second embodiment (see FIGS. 4 and 5) on the pull rod loaded by a tension spring.
The front jaw enables, in both embodiments, a good fastening of differently constructed soles of boots on the ski. A release of the ski boot, however, does not take place during a backward fall of the skier.